The Effectiveness of Real-Time PCR Assay, Compared with Microbiologic Results for the Diagnosis of Pulmonary Tuberculosis

Abstract

BackgroundThe incidence of tuberculosis (TB) in Korea is relatively high compared to the other Organisation for Economic Co-operation and Development (OECD) countries, with a prevalence of 71 per 100,000 in 2012, although the incidence is declining. Real-time polymerase chain reaction (PCR) has been introduced for the rapid diagnosis of TB. Recently, its advantage lies in higher sensitivity and specificity for the diagnosis of TB. This study evaluated the clinical accuracy of real-time PCR using respiratory specimens in a clinical setting.MethodsReal-time PCR assays using sputum specimens and/or bronchoscopic aspirates from 2,877 subjects were reviewed retrospectively; 2,859 subjects were enrolled. The diagnosis of TB was determined by positive microbiology, pathological findings of TB in the lung and pleura, or clinical suspicion of active TB following anti-TB medication for more than 6 months with a favorable response.ResultsSensitivity, specificity, and accuracy were 44%, 99%, and 86% from sputum, and 65%, 97%, and 87% from bronchoscopic aspirates, respectively. For overall respiratory specimens, sensitivity was 59%, specificity was 98%, and accuracy increased to 89%.ConclusionPositivity in real-time PCR using any respiratory specimens suggests the possibility of active TB in clinically suspected cases, guiding to start anti-TB medication. Real-time PCR from selective bronchoscopic aspirates enhances the diagnostic yield much more when added to sputum examination.

Real-Time Polymerase Chain Reaction Assay: A Response to Recent Letter to the Editor

“…As a response to the issues of false-positivity raised by Wiwanitkit 1 , it was mentioned in our paper 2 that "In our study, the false-positive rate was 0.5% in sputum and 2.0% in bronchoscopic aspirates. False-positivity in PCR has been reported to be due to carry-over contamination between specimens, cross-reactions with isolated nontuberculous mycobacteria, or dead tissue debris from previous TB scarring in highly endemic areas."…”

“…Low sensitivity of this test was also discussed in our paper 2 that "Most reports have evaluated PCR using known acid-fast bacilli-positive samples. In smear-positive specimens, the sensitivity and specificity of polymerase chain reaction are in the range 90%-100%, with a positive predictive value of >95%, whereas in smear-negative specimens, the sensitivity of PCR is reduced to <50%.…”

“…Thank you for the recent comments 1 for the topic of real-time polymerase chain reaction (RT-PCR) assay 2 . We propose that positivity in RT-PCR using any respiratory specimens suggests the possibility of active tuberculosis (TB) in clinically suspected cases, guiding to start anti-TB medication, and RT-PCR from selective bronchoscopic aspirates enhances the diagnostic yield much more when added to sputum examination 2 . Wiwanitkit 1 mentioned that "There are some concerns on this assay.…”

Real-Time Polymerase Chain Reaction Assay for the Diagnosis of Pulmonary Tuberculosis

“…To the editor: The recent report on "Real-time polymerase chain reaction (PCR) assay for the diagnosis of pulmonary tuberculosis" is very interesting 1 . Kim et al 1 noted that "Real-time PCR from selective bronchoscopic aspirates enhances the diagnostic yield much more when added to sputum examination." In fact, polymerase chain reaction assay for tuberculosis (TB) is considered new and useful diagnostic test.…”

“…First, false-positive of the test can be seen in cases with "treated or old lesion from pulmonary TB 2 ." Second, the low sensitivity of the test can be seen 1 2 3 . In fact, there are many possible causes of low sensitivity including to type of specimen transfer and duration time, the DNA extraction procedure, DNA amplified process, DNA extraction, and reproducible technique 2 .…”